It has become quite clear that in order to understand the intricacies of biochemical events taking place within cells that lead to the synthesis of eicosanoids such as prostaglandins and leukotrienes, one must have a means by which one can measure virtually all products of these pathways. The development of analytical techniques have kept pace with our understanding of these needs so that extraordinarily powerful tools are now available. Mass spectrometry has emerged as the technique of choice based on sensitivity and specificity demanded by the projects proposed in this application. Advances in electro-spray ionization and tandem mass spectrometry when coupled to liquid chromatography (LC/MS), has made it possible to carry out 30 targeted eicosanoids, or more, in a single LC/MS/MS experiment. Capillary gas chromatography/mass spectrometry (GC/MS) remains an unparalleled technique in its capability to identify and quantitate fatty acids (as many a 20 fatty acids in a single experiment). Based on this state of the art technology, the major specific aims of this core are to provide state of the art assays for target lipids on a routine basis to facilitate investigations in each of the individual research projects within the Center proposal. Specifically: 1) liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (LC/MS/MS) will be used to quantitate metabolites of arachidonic acid and eicosapentaenoic acid by the cyclooxygenase and 5- and 12/15-lipoxygenase pathway and 2) Gas chromatography/mass spectrometry (GC/MS) will be used to quantitate and identify fatty acids, including polyunsaturated fatty acids in biological extracts.